Magnetic recording medium including a diamond-like carbon protective film and at least two additional elements

ABSTRACT

A magnetic recording medium having a diamond-like carbon (DLC) film added therein a Group IV element of the periodic table such as silicon, particularly in the vicinity of the boundary between the magnetic material and the formed DLC film. Since a DLC having low friction coefficient can be formed, the centerline average roughness can be reduced to 30 nm or even less. Accordingly, a magnetic recording medium improved in magnetic properties and in lubricity can be obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic recording medium such as anaudio and a video tape, a floppy diskette, and a hard disk. Inparticular, the present invention relates to a technique for coatingmagnetic thin films to provide magnetic recording media having improvedproperties.

2. Prior Art

A magnetic recording medium such as an audio and a video tape, a floppydiskette, and a hard disk is generally constructed by forming a magneticfilm on a substrate support made of an organic resin or a metal and thelike. The magnetic film is formed by coating or by a vacuum process suchas vapor deposition and sputtering. If the process cost is the matter ofconcern, coating is the choice in forming the magnetic film, and if highperformance is required on the obtained film, a vacuum process isselected.

When in use, magnetic recording media are under a mechanical loadbecause they are constantly or temporarily brought into contact with amagnetic head (an apparatus for writing and reading signals) or amechanical component thereof, and with mechanical parts such as acapstan and a roller. Accordingly, not only magnetic properties but alsomechanical durability and lubricity are required to the magneticrecording media to resist the above mechanical load. Conventionally,attempts had been made to lower the friction coefficient of the magneticmedia, for example, by applying a lubricant coating to the surface ofthe magnetic film, or by forming irregularities on the surface tosubstantially reduce the contact area between the contact member and themagnetic film. However, the lubricant film suffers wear by repeatedcontact and sliding, to result in an increase of the frictioncoefficient thereof. Accordingly, the degradation proceeds in anaccelerated manner.

Recent trend treats information which had been conventionally analogsignals such as images and sound as digital signals. Accordingly, thereliability of magnetic recording medium on recording is required. Undersuch circumstances, the friction coefficient of a magnetic recordingmedium must be maintained stably at a low level.

A magnetic thin film is formed by either coating a substrate with amixture of a powder of a magnetic material and an organic polymer, or byforming a layer of the magnetic material alone on a substrate by avacuum process such as vapor deposition and sputtering. Thin filmshaving better magnetic properties can be obtained by a vacuum process.The magnetic material is generally a ferrite or a metal, etc. Metallicmagnetic materials specifically include NiCo and CoPtCr alloys.

Alternatively, methods for forming a hard coating of carbon or amaterial containing carbon as the principal component by plasma CVDprocess are disclosed, for example, in JP-B-3-72711, JP-B-4-27690, andJP-B-4-27691 (the term “JP-B-” as referred herein signifies an “examinedJapanese patent publication”). Those well known processes compriseintroducing a hydrocarbon gas and a hydrogen gas as material gasesinside a vessel maintained under a reduced pressure, applying generallya high frequency electric field to a pair or more electrodes installedinside the vessel, and forming a plasma of the material gas to therebyactivate and deposit grains containing carbon on the substrate.

The coating thus obtained is called diamond-like carbon (abbreviated asDLC hereinafter) because it is extremely hard and exhibits diamond-likecharacteristics. In general, DLC is deposited by applying self bias or abias from an external power supply, so that a negative bias with respectto the plasma potential may be applied to the substrate. In this manner,the bonds having the graphite-like characteristics (attributed to thecombination of sp² hybrid orbital and p orbital) within the carbon filmare etched to leave mainly the bonds exhibiting the diamond-likecharacteristics attributed to sp³ hybrid orbital.

Such a DLC thin film is very hard as to yield a Vicker's hardness of2,000 kg/mm² or even higher, and is also low in friction coefficient.Accordingly, the DLC film is suited as a protective and lubricant filmto coat the surface of a magnetic film.

When applied to the surface of a magnetic material, and particularly tothe surface of a metallic magnetic material, however, the aforementionedDLC film easily undergoes separation after film deposition, or sufferspeeling off upon bringing it in contact with or sliding it against amechanical component. The DLC films were not practically feasible,therefore, due to their insufficiently low adhesion strength.

SUMMARY OF THE INVENTION

Under the light of the circumstances above, the present inventionprovides a magnetic thin film having thereon a coating containing carbonas the principal component, added therein an element selected from thegroup consisting of boron, aluminum, gallium, nitrogen, phosphorus andarsenic. Alternatively, the present invention provides a magnetic thinfilm having thereon a coating of pure carbon or a coating containingcarbon as the principal component, added therein 20% by atomic or lessof an element belonging to Group IV of the periodic table (referred tosimply hereinafter as a “Group IV element”). More specifically, a GroupIV element includes Si and Ge, Sn (tin) and Pb (lead).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically the layer structure of a magnetic recordingmedium;

FIG. 2 shows schematically an apparatus for plasma-assisted CVD of apositive column type;

FIG. 3 shows an infrared spectrogram obtained by FT-IR (Fouriertransform infrared spectroscopy) analysis for a DLC film containingsilicon;

FIG. 4 shows a Raman spectrogram obtained for a DLC film containingsilicon;

FIG. 5 shows the dependence of initial friction coefficient on the filmthickness of a DLC film;

FIG. 6 shows the dependence of friction coefficient after passage oftime on the film thickness of a DLC film;

FIG. 7 shows an infrared spectrogram obtained by FT-IR (Fouriertransform infrared spectroscopy) analysis for a DLC film with no siliconadded therein;

FIG. 8 shows a Raman spectrogram obtained for a DLC film with no siliconadded therein;

FIG. 9 is a schematic view showing a roll-to-roll type apparatus forforming a DLC film; and

FIGS. 10(A) and 10(B) are graphs each showing an impurity concentrationprofile.

DETAILED DESCRIPTION OF THE INVENTION

The reason why the adhesibility of a DLC film according to the presentinvention increases can be explained as follows. A DLC film containsboth a bond having graphite-like characteristics (attributed to thecombination of an sp² hybrid orbital and a p orbital) and a bondexhibiting diamond-like characteristics (attributed to an sp³ hybridorbital). In an sp³ hybrid orbital, four σ electrons contribute to thebond, but in a combination of an sp² hybrid orbital and a p orbital,three σ electrons and one π electron form a bond. Since the bond forceis lower for the bond attributed to π electron as compared with thatwith σ electrons being incorporated, a DLC film containing sp³ hybridorbital at a higher fraction results in a higher hardness more nearer tothe properties of a diamond. The same holds in a case applied to theboundary with a metal, and hence a more favorable adhesion or a higherbonding force can be realized by reducing as possible the number ofcarbon atoms based on a combination of sp² hybrid orbital and p orbital.

In contrast to the above, it is well established that silicon atoms takeonly the sp³ hybrid orbital state (four-coordinated). It is also wellknown that when a three- or five-coordination element is added aloneinto the four-coordinated elements, the added element accommodate itselfinto a more thermally stable four-coordination. Specifically, thisphenomenon can be observed by adding P (phosphorus) or B (boron) as adopant into Si (silicon), because the added P or B changes into afour-coordinated state. More specifically, when a silicon atom whichtakes only the four-coordination state is added to the vicinity of athree-coordinated (attributed to the combination of an sp² hybridorbital and a p orbital) carbon atom, the carbon atom changes itselfinto a four-coordinated state to increase the fraction of carbon atomshaving the sp³ hybrid orbital as a result. Assumably in this manner, theadhesibility of a DLC film added therein silicon atoms is increased.

The silicon atoms are preferably added into the DLC at an amount of 20%by atomic or less, and more preferably, from 1 to 15% by atomic. Ifsilicon is added excessively into DLC, the fractions of C—Si and Si—Sibonds increase to reversely decrease the amount of C—C bonds. Thepresence of excessively large amount of C—Si and Si—Si bonds in the DLCfilm affects the film to yield silicon-like properties. Accordingly, itresults in a low hardness and an increase in friction coefficient.Silicon must be added within an optimal range of addition.

The DLC film contains hydrogen in addition to carbon and silicon. Thisis because hydrocarbon is used as the starting gas material, but incases, hydrogen is positively added into the gas material. The hydrogenatoms inside the film function as terminators of the dangling bonds toimprove the electric and optical properties as well as the thermalstability of the resulting film. The DLC film according to the presentinvention also contains from 10 to 60% by atomic, and preferably, from15 to 40% by atomic of hydrogen.

Elements belonging to Group III or Group V of the periodic table(referred to simply hereinafter as Group III or Group V element) may beadded additionally into the DLC film. Specifically mentioned as theGroup III elements are boron, aluminum, and gallium; Group V elementsinclude specifically nitrogen, phosphorus, and arsenic. Those additionalGroup III or Group V elements function in such a manner to relax theinternal stress of the DLC film. Since the adhesibility of the entirefilm largely depends on the adhesion strength at the boundary betweenthe DLC film and the magnetic material, the internal stress of the DLCitself can be lowered to improve the adhesibility of the entire film. Inother words, the internal stress of the DLC film itself, which functionsas the drive force to cause peeling of the film off the magneticmaterial, is relaxed.

The magnetic material of the present invention comprises a metal ormetal alloy such as Fe, Co, Ni, and an alloy thereof (e.g. Co—Ni alloy).Alternatively, the magnetic material of the present invention comprisesa metal oxide such as γ-Fe₂O₃, CrO₂ and Co-γ-FeO_(x).

The concentration of silicon atoms inside DLC may be constant along thedepth direction of the film, buy it is more preferred that theconcentration of silicon atoms is gradually increased with increasingdepth from the surface of the film. This is because the frictioncoefficient increases with increasing fraction of the sp³ bonds andhence with increasing concentration of silicon atoms. Thus, the DLC filmis preferably separated into at least two layers of differing functionsby adding silicon to the portion in the vicinity of the boundary toincrease the sp³ fraction and hence the adhesibility thereof, while notadding any silicon to the surface portions to which low frictioncoefficient is required. A function-separated type DLC film is preferredfor the application on a magnetic thin film.

For example, the DLC film may have an impurity (e.g. silicon, germanium,tin and lead) concentration profile as shown in FIG. 10(A) or FIG.10(B). The impurity concentration is increased from the boundary of themagnetic film and the DLC film to a surface of the DLC film, and alsothe impurity concentration in a portion of the DLC film near the surfaceof the DLC film is larger than that near the boundary, as shown in FIGS.10(A) and 10(B).

A DLC film improved in adhesibility by the method described above wassubjected to an experiment. It was confirmed by the experiment that thesurface irreguralities employed in the prior art technique becomesunnecessary in the present invention by virtue of the DLC film. It wastherefore found possible to considerably improve the magnetic propertyof the magnetic recording medium by reducing the distance between themagnetic head and the magnetic material. The reason for these effects isexplained below.

Assuming that the magnetization per unit area is generally constant, theS/N ratio increases with decreasing distance between the magnetic headand the magnetic material. If the distance between the magnetic head andthe magnetic material is sufficiently short, on the contrary, themagnetic flux attributed to a S/N ratio higher than a specified levelcan be reduced. Accordingly, it can be seen that the reliability ofrecording can be improved by bringing the magnetic head to a position asnear as possible to the magnetic material.

A prior art magnetic recording medium had surface irregularities tolower the friction coefficient of the surface. By providing the surfaceof the film with irregularities, the effective area of contact can bereduced and lower the friction coefficient thereof. But this measure is,so to say, giving priority to the lowering of friction coefficient atthe expense of favorable magnetic properties.

In contrast to the above, the present invention allows both of theconflicting properties to stand at the same time. More specifically, thepresent invention lowers the friction coefficient between the surface ofthe magnetic recording medium and various mechanical components whileimproving reliability of recording.

According to the experiment of the present inventors, a frictioncoefficient of the surface of the magnetic material without a DLCcoating was found to be about 0.4 in case a centerline average roughnessRa is 30 nm, and 0.8 with an Ra of 10 nm. Since a practically feasiblevalue for the friction coefficient is 0.4 or lower, at least an Ra of 30nm is necessary for a case no DLC coating is formed on the magneticmaterial. In contrast to these results, the surface of a magneticmaterial coated with an DLC was found to yield a friction coefficient ina low level range of from 0.2 to 0.4 even at an Ra of 10 nm. Moreover,the material coated with DLC was found to yield a stable frictioncoefficient even after subjecting it to repeated sliding motion.

Experimental results revealed that the friction coefficient depends onthe film thickness of DLC, that is, the friction coefficient isdecreased as the thickness of DLC increases. A practical frictioncoefficient can be obtained on a DLC film with a thickness of 10 to 200Å.

It can be seen that the magnetic properties of a film can be improved byapplying the present invention, yet maintaining the friction coefficientto a low level and reducing the surface irregularities.

The process for fabricating a DLC coating is described below.

DLC can be produced by plasma CVD process as described hereinbefore inthe description of prior art. The plasma CVD process can be performed byeither a general process using parallel planar electrodes or a positivecolumn type plasma CVD which utilizes the positive column portion of theplasma. The application of the process using parallel planar electrodesis restricted to flat substrates, but the process using the positivecolumn is applicable to three-dimensional structures. It can be seenthat the process using a positive column is advantageous because it isapplicable to any substrate having a desired shape and because it issuited for mass production.

When a planar substrate is used, it is set to a substrate holder andthen maintained inside a reaction chamber. If a film substrate is used,it is introduced into vacuum in a rolled shape, and then run through thereaction chamber by taking it up from a roll to another roll.

Hydrocarbon can be used as the reaction gas for the carbon source.Hydrocarbons for use in the process include a saturated hydrocarbon(e.g., methane, ethane, propane, and butane), an unsaturated hydrocarbon(e.g., ethylene and acetylene), and an aromatic hydrocarbon (e.g.,benzene and toluene). Adamantane, adamantanol, etc., may be used aswell. Furthermore, halogenated hydrocarbons containing halogens such asfluorine, chlorine, and bromine as substituents substituting for one ora plurality of hydrogen atoms may be used.

The reactive gas may also contain hydrogen in addition to hydrocarbons.The hydrogen radicals inside the plasma can be increased by addinghydrogen to the reactive gas, and hence, hydrogen atoms present in thefilm in excess are expected to be pulled out from the film. Accordingly,a film with further improved quality can be obtained. Hydrogen is flownwith the reactive gas at a flow ratio of from 30 to 90%, preferably 50to 70% with respect to the total gas flow. If the ratio of the hydrogengas flow to the total gas flow should be too high, the film depositionrate would be decreased. If the ratio should be too low, on thecontrary, the function of pulling out excessive hydrogen from the filmwould not be expected any more.

To add a Group IV element, i.e., silicon, compounds such as silane,disilane, fluorine-containing silane, etc., may be used. In addinggermanium, useful gases include germane and fluorine-containing germane.A Group III element can be added by using diborane, boron trifluoride,trimethylborane, etc. A Group IV element can be added by using N₂,ammonia, nitrogen trifluoride, etc., in case of adding nitrogen; and toadd phosphorus, phosphine and the like can be used. The flow ratio ofthose gases depend on other film deposition parameters such as thepressure and the applied electric power, but in general, the flow ratiois preferably controlled to a ratio of 10% or less with respect to theflow ratio of the carbon source gas.

Then, the reactive gas is introduced inside the reaction vessel, thepressure thereof is controlled to a predetermined value, and a highfrequency electric power is applied to a pair or a plurality ofelectrodes installed inside the reaction vessel. A total reactive gasflow rate of 30 sccm or higher, preferably 50 sccm or higher, isnecessary for a reaction chamber having a volume of about 0.02 m³. Theupper limit of the total flow depends on the evacuation rate of theevacuation system, but a gas flow with a lower limit as above must bemaintained.

The reaction pressure is in the range of from 5 to 1,000 mTorr,preferably in the range of from 10 to 100 mTorr. In general, a highfrequency power with a frequency of 13.56 MHz is used. The appliedelectric power is preferably in the range of from 0.01 to 1 W/cm², andmore preferably in the range of from 0.05 to 0.5 W/cm².

The substrate need not be heated. This is a merit in applying theprocess to mass production.

In depositing a DLC film, it is advantageous to apply an electric fieldto the reaction chamber in such a manner that the particles, mainlyions, inside the plasma would be incident on the surface of thesubstrate. A hard and dense film can be obtained as a result. In thecase a plasma CVD based on a parallel planar electrodes method is used,a blocking capacitor may be installed on the electrode on the side forsupplying an RF power to generate self bias, so that it may be used togenerate the electric field to guide the ions incident to the surface ofthe substrate. In this case, the substrate is placed on the side forsupplying the RF power.

In a case positive column type plasma CVD apparatus is used, an externalelectric power source must be used to generate the aforementionedelectric field, because ions would not be incident on the substrate ifthe substrate is set simply inside the positive column. AC is effectiveas an electric field applied from an external power source. Thefrequency is preferably controlled to be in the range between the ionplasma frequency and the electron plasma frequency inside the plasma.The ion plasma frequency yields a value about several digits smallerthan the electron plasma frequency ascribed to the difference in mass ofthe ion and the electron. If an external electric field with a frequencylower than the electron plasma frequency but higher than the ion plasmafrequency is applied, the ions would not be able to move sufficiently tofollow the external electric field, but the electrons would follow theexternal electric field. In this manner, a substrate having a surfacenegatively charged up can be obtained. As a result, an electric fieldthat would allow the ions to be incident on the surface of the substratemay be generated, and a hard and dense DLC film would be obtained by thereaction between the incident ions and the film surface. The frequencyof the external electric field for applying bias depends on thetemperature and density of the electrons as well as the temperature anddensity of the ions inside the plasma, but preferably, it is in therange of from 1 to 1,000 kHz, and more preferably, in the range of from10 to 500 kHz. The peak to peak intensity of the electric field is inthe range of from 50 to 1,000 V, and preferably from 100 to 400 V.

Furthermore, in the case of a metallic magnetic thin film is depositedby a vapor deposition process according to the present invention, inparticular, it has excellent adhesibility with a carbon film addedtherein a Group IV element.

EXAMPLE 1

The present embodiment relates to a magnetic recording medium formed ona film substrate. FIG. 1 shows the layer structure of the magnetic filmfabricated by a process according to the present example.

A magnetic film 12 was deposited on the surface of a support substrate,a 7 μm thick polyethylene terephthalate (PET) film 11 having acenterline average roughness Ra of 3 nm and being supplied as a roll 400nm in width. A CoNi alloy was used as the magnetic film 12. A 200 nmthick film was obtained by vacuum deposition. A DLC film 13 was thendeposited on the magnetic film 12, varying the thickness within a rangeof from 10 nm to 50 nm.

The DLC film was deposited using a CVD apparatus of a positive columntype. A pair of electrodes 22 as shown with broken lines in FIG. 2 wereinstalled inside a vacuum vessel 21, and an RF power was supplied to theelectrodes 22 from an RF power source (not shown in FIG. 2) via amatching box (not shown in FIG. 2) to form a plasma inside a reactionchamber 25. As material gases, methane and hydrogen gases were suppliedat a flow rate of 50 sccm each. Otherwise, they were supplied at a rateof 30 sccm and 70 sccm, respectively. The pressure was controlled to 10mTorr. An RF power of 100 W was applied.

To add silicon at the boundary between DLC and the magnetic film, SiH₄gas was added to the reactive gas for a duration corresponding to 10% ofthe entire duration of reaction, i.e., for a period of 1 minute. The gaswas supplied at a flow rate of 2.5 sccm.

The substrate film 26 was supplied from a feed roll 26, and taken upusing a take-up roll 27. The film was subjected to a plurality of turnsinside the reaction chamber 25 by rolls 28 to effectively use thereaction chamber, thereby increasing the through put.

A bias electrode 29 was set in contact with the back plane of the filmto apply thereto a bias electric field, The bias potential frequency was50 kHz, and the bias potential expressed by peak to peak value was 200V.

At the same time, a silicon wafer was set inside the same batch tomonitor the film quality. The film quality of the deposited film thusobtained as a sample was evaluated to obtain a Knoop hardness of 2,500kg/mm². The infrared (IR) spectrogram obtained by FT-IR analysis and theRaman spectrogram for the sample are given in FIGS. 3 and 4,respectively. The FT-IR analysis reveals the presence of an absorptionband in the wavenumber range of from 700 to 800 cm⁻¹ assigned to Si—Cbond, and an absorption assigned to Si—H bond at ca. 2,100 cm⁻¹. Ramanspectrogram reads a broad scattered light peak at ca. 1,550 cm⁻¹characteristic of DLC. It can be seen from those results that Si isadded while maintaining the structure of a DLC.

The friction coefficient of the magnetic tape obtained in the presentExample was measured by coiling the tape for half the periphery of a3-mm diameter stainless steel pin, and applying a load of 20 g at asliding speed of 428 mm/min for a distance of 50 mm.

The initial friction coefficient thus obtained is plotted against thefilm thickness of DLC in FIG. 5. The graph reads that initial frictioncoefficient depends on the film thickness in case a CH₄ concentrationwas controlled to 30%. A high friction coefficient of 0.44 is obtainedat a film thickness of 15 nm, and the friction coefficient lowers withincreasing film thickness. A practical friction coefficient of 0.4. orlower is obtained at a film thickness of about 20 nm. No film thicknessdependence is obtained at a CH₄ concentration of 50%, and a value of 0.3or lower is obtained even at a film thickness of 15 nm.

The change of friction coefficient with passage of time is plottedagainst film thickness in FIG. 6. The change in value is the incrementof friction coefficient after repeated sliding of 200 times with respectto the initial friction coefficient. It can be observed from FIG. 6 thatthe value depends on the film thickness irrespective of theconcentration of CH₄, and that the change decreases with increasing filmthickness. From a practical viewpoint, it is desired that no change isfound in friction coefficient with passage of time. However, if thefriction coefficient is limited to a value of 0.4 or lower, a change infriction coefficient with passage of time of 0.1 or lower and that of 0or lower are desired for a CH₄ concentration of 50% and 30%,respectively. Thus, a film thicknesses of 27 nm or more and 21 nm ormore are desired for cases with CH₄ concentration of 50% and 30%,respectively.

It can be seen from the foregoing discussion on the initial frictioncoefficient and the friction coefficient with passage of time that filmthicknesses of 27 nm or more and 21 nm or more are necessary for caseswith CH₄ concentration of 50% and 30%, respectively.

It is well-known that a signal level decreases by 1 dB for an incrementof 10 nm in the distance between the magnetic head and the magneticfilm. If a DLC film is deposited at a thickness sufficiently thick toassure a practically useful friction coefficient on a substrate having asurface roughness of 3 nm being used in the present example, a drop of 3dB and that of 2.4 dB result in cases using DLC containing CH₄ at aconcentration of 50% and 30%, respectively.

Considering a conventional process, on the other hand, a surfaceirregularity of 30 nm and a lubricant film 10 nm or more in thicknessare necessary. Then, a drop of 4 dB or more in signal level results forthe overall film structure. This signifies that the use of the DLC filmaccording to the present invention improves the level for 1 dB or moreas compared to a case according to prior art.

COMPARATIVE EXAMPLE

A DLC film containing no silicon was prepared to compare with the DLCfilm obtained in the above example. The same magnetic film and thefabrication process as those of the above Example were used, except foradding no silane gas into the starting gas material. The resultsobtained by FT-IR analysis and Raman spectroscopy are given in FIGS. 7and 8. Raman spectrogram shows that the film is a typical DLC film, andit can be observed from the FT-IR spectrogram that no Si is incorporatedin the film.

Peeling occurred autogenously on the DLC formed on the magnetic film,and no film could be obtained.

It can be seen from the foregoing results that a DLC film can bedeposited as a protective or lubricant film on a magnetic recordingmedium with improved adhesibility to the magnetic material by addingsilicon. Furthermore, since the surface irregularities can be reduced bydepositing the DLC film of the present invention, the magneticproperties can be improved by 1 dB or more as compared with the priorart magnetic recording media.

The present invention was explained referring specifically to a processwhich comprises depositing a DLC film using a CVD apparatus of apositive column type. However, the effect of the present invention isnot limited by the method of film deposition. Accordingly, though notdescribed in the above Example, the film can be deposited by using a CVDapparatus equipped with parallel planar electrodes, or by using carbonion beam.

Furthermore, the present invention was described to a specific caseusing silicon as an additive to improve the adhesibility of the DLCfilm. However, similar improved film adhesion strength can be achievedby using other Group IV elements such as germanium, tin and lead.

The DLC film of the present invention can be formed by a CVD apparatusillustrated in FIG. 9 instead of the CVD apparatus shown in FIG. 2.Referring to FIG. 9, the apparatus comprises insulators 51, 52, 53, 54,55, and 56, a can roll 31 acting as a cathode electrode, a feed roll 33,a take-up roll 32, guide rolls 34, an RF power source 35 connected tothe can roll 31 through a blocking capacitor 58, exhausting pipes 36,37, 38, 39, 42, 45 and 47 connected to a vacuum pump, a gas supplyingpath 40 extending to a discharging space 44 through inside of an anode43, a space 41 for forming a DLC film therein, a space 49 for hydrogenplasma treatment, and a gas supplying path 50 extending to a dischargingspace 48 through inside of an anode 46. A film substrate 57 havingprovided thereon a magnetic material layer is supplied from the feedroll 33, and taken up by the take-up roll 32. The space 49 and thedischarging space 48 are evacuated by the vacuum pump through theexhausting pipe 47 and supplied with a H₂ gas from the gas supplyingpath 50 to maintain a pressure of the space 49 and the discharging space48 from 60 to 100 Pa e.g. 80 Pa. The space 41 and the discharging space44 are evacuated by the vacuum pump through the exhausting pipe 42 andsupplied with an ethylene gas and a H₂ gas from the gas supplying path40 to maintain a pressure of the space 41 and the discharging space 44from 60 to 100 Pa e.g. 80 Pa. The anodes 43 and 46 are, for example,grounded. The cathode electrode, i.e. the can roll 31 is supplied withan RF electric energy from the RF power source 35 e.g. at 13.56 MHz. Inthis way, a discharge is caused between the can roll (cathode) 31 andthe anode 46, and also a discharge id caused between the can roll(cathode) 31 and the anode 43. The film substrate 57 is then subjectedto a hydrogen plasma treatment in the discharging space 48, and to adeposition of the DLC film on the magnetic material layer in thedischarging space 44. The distance between the surface of the can roll31 and the surface 59 of the anode 43, and the distance between thesurface of the can roll and the surface 60 of the anode 46 are 20 mm orless, e.g. 18 mm or less. The distance 61 between the surface of the canroll 31 and each of the surfaces of the insulators 51, 52, 55 and 5 is 5mm or less, e.g. 2 mm or less.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A system comprising: a magnetic medium; and a magnetic head to be incontact with the magnetic medium constantly or temporarily, wherein themagnetic medium comprises a magnetic layer and a protective filmcomprising diamond-like carbon, wherein the protective film contains afirst element selected from the group consisting of silicon, germanium,tin and lead at a concentration of 20 atomic % or less, wherein theprotective film contains a second element which belongs to Group III orGroup V of the periodic table, wherein a concentration of the firstelement at a first portion of the protective film is higher than aconcentration of the first element at a second portion of the protectivefilm.
 2. The system according to claim 1, wherein the diamond-likecarbon has carbon bonds attributed to sp³ hybrid orbital.
 3. The systemaccording to claim 1, wherein a friction coefficient of a surface of theprotective film is 0.4 or less.
 4. The system according to claim 1,wherein the magnetic medium is selected from the group consisting of anaudio tape, a video tape, a floppy disk and a hard disk.
 5. The systemaccording to claim 1, wherein the concentration of the first element ata bottom of the protective film is higher than a concentration of thefirst element at a surface of the protective film.
 6. A systemcomprising: a magnetic medium; and a magnetic head to be in contact withthe magnetic medium constantly or temporarily, wherein the magneticmedium comprises a magnetic layer and a protective film comprisingdiamond-like carbon, wherein the protective film contains a firstelement selected from the group consisting of silicon, germanium, tinand lead at a concentration of 20 atomic % or less, wherein theprotective film contains a second element which belongs to Group III orGroup V of the periodic table, wherein a concentration of the firstelement at a first portion of the protective film is higher than aconcentration of the element at a second portion of the protective film,and wherein the protective film contains hydrogen at a concentration ina range of 10 to 60 atomic %.
 7. The system according to claim 6,wherein the diamond-like carbon has carbon bonds attributed to sp³hybrid orbital.
 8. The system according to claim 6, wherein a frictioncoefficient of a surface of the protective film is 0.4 or less.
 9. Thesystem according to claim 6, wherein the magnetic medium is selectedfrom the group consisting of an audio tape, a video tape, a floppy diskand a hard disk.
 10. The system according to claim 6, wherein theconcentration of the first element at a bottom of the protective film ishigher than a concentration of the first element at a surface of theprotective film.
 11. A system comprising: a magnetic medium; and amagnetic head to be in contact with the magnetic medium constantly ortemporarily, wherein the magnetic medium comprises a magnetic layer anda protective film comprising diamond-like carbon, wherein the protectivefilm contains a first element selected from the group consisting ofsilicon, germanium, tin and lead at a concentration of 20 atomic % orless, wherein the protective film contains a second element whichbelongs to Group III or Group V of the periodic table, wherein aconcentration of the first element at a first portion of the protectivefilm is higher than a concentration of the element at a second portionof the protective film, and wherein a center line average roughness ofthe protective film is 30 nm or less.
 12. The system according to claim11, wherein the diamond-like carbon has carbon bonds attributed to sp³hybrid orbital.
 13. The system according to claim 11, wherein a frictioncoefficient of a surface of the protective film is 0.4 or less.
 14. Thesystem according to claim 11, wherein the magnetic medium is selectedfrom the group consisting of an audio tape, a video tape, a floppy diskand a hard disk.
 15. The system according to claim 11, wherein theconcentration of the first element at a bottom of the protective film ishigher than a concentration of the first element at a surface of theprotective film.
 16. A system comprising: a magnetic medium; and amagnetic head to be in contact with the magnetic medium constantly ortemporarily, wherein the magnetic medium comprises a magnetic layer anda protective film comprising diamond-like carbon, wherein the protectivefilm contains a first element selected from the group consisting ofsilicon, germanium, tin and lead at a concentration of 20 atomic % orless, wherein the protective film contains a second element whichbelongs to Group III or Group V of the periodic table, wherein aconcentration of the first element at a first portion of the protectivefilm is higher than a concentration of the element at a second portionof the protective film, and wherein Vicker's hardness of the protectivefilm is 2000 kg/mm² or more.
 17. The system according to claim 16,wherein the diamond-like carbon has carbon bonds attributed to sp³hybrid orbital.
 18. The system according to claim 16, wherein a frictioncoefficient of a surface of the protective film is 0.4 or less.
 19. Thesystem according to claim 16, wherein the magnetic medium is selectedfrom the group consisting of an audio tape, a video tape, a floppy diskand a hard disk.
 20. The system according to claim 16, wherein theconcentration of the first element at a bottom of the protective film ishigher than a concentration of the first element at a surface of theprotective film.
 21. A system comprising: a magnetic medium; and amagnetic head operationally connected with the magnetic medium, whereinthe magnetic medium comprises a magnetic layer and a protective filmcomprising diamond-like carbon, wherein the protective film contains afirst element selected from the group consisting of silicon, germanium,tin and lead at a concentration of 20 atomic % or less, wherein theprotective film contains a second element which belongs to Group III orGroup V of the periodic table, wherein a concentration of the firstelement at a first portion of the protective film is higher than aconcentration of the first element at a second portion of the protectivefilm.
 22. The system according to claim 21, wherein the diamond-likecarbon has carbon bonds attributed to sp³ hybrid orbital.
 23. The systemaccording to claim 21, wherein a friction coefficient of a surface ofthe protective film is 0.4 or less.
 24. The system according to claim21, wherein the magnetic medium is selected from the group consisting ofan audio tape, a video tape, a floppy disk and a hard disk.
 25. Thesystem according to claim 21, wherein the protective film containshydrogen at a concentration in a range of 10 to 60 atomic %.
 26. Thesystem according to claim 21, wherein a center line average roughness ofthe protective film is 30 nm or less.
 27. The system according to claim21, wherein Vicker's hardness of the protective film is 2000 kg/mm² ormore.
 28. The system according to claim 21, wherein the concentration ofthe first element at a bottom of the protective film is higher than aconcentration of the first element at a surface of the protective film.